1. Field of the Invention
The present invention relates to a numerical controller and particularly to a numerical controller having an error compensation function in consideration of an axis movement direction.
2. Description of the Related Art
An error occurs between a target position and an actual movement position of a feed shaft of a machine tool controlled by a numerical controller. Since the amount of the error becomes different by each movement position, a method of compensating the error in response to the movement position has been proposed in the past.
For example, JP 2009-151756 A discloses a technique of dividing a linear axis coordinate system and a rotation axis coordinate system into latticed areas, storing lattice point compensation vectors in lattice points, calculating an axis dependent translation compensation amount and an axis dependent rotation compensation amount from a linear axis position and a rotation axis position based on the lattice point compensation vector, and compensating the linear axis position.
The above-described technique can compensate an error of a tool center point caused by an error at a previously measured machine position. However, since a space error map is created for a compensation based on only position information, an error difference occurring in a movement direction (a positive direction and a negative direction) of a machine caused by degradation of a driving portion cannot be accurately compensated.
Further, JP 07-072913 A discloses a technique of storing pitch error compensation amounts in both positive and negative movement directions every preset compensation section and reading a compensation amount in response to a movement direction and a compensation section including a current position and outputting the read compensation amount.
The above-described technique can compensate an error in consideration of the positive/negative movement direction. However, only each axis can be compensated separately.